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TitleGeospatial modelling of shear-wave velocity and fundamental site period of Quaternary marine and glacial sediments in the Ottawa and St. Lawrence Valleys, Canada
AuthorNastev, M N; Parent, M P; Ross, M R; Howlett, D H; Benoit, N B
SourceSoil Dynamics and Earthquake Engineering vol. 85, 2016 p. 103-116,
Alt SeriesEarth Sciences Sector, Contribution Series 20140235
Mediapaper; on-line; digital
File formatpdf
ProvinceOntario; Quebec
NTS31B; 31G; 31H; 31I; 21L
AreaSt-Lawrence lowlands
Lat/Long WENS -76.0000 -70.0000 47.0000 45.0000
Subjectssediments; overburden thickness; velocity surveys; geological research; fundamental site period; geological modelling
Illustrationslocation maps; geological sketch maps; stratigraphic columns; histograms; graphs; plots
ProgramQuantitative risk assessment project, Public Safety Geoscience
Released2016 04 06
AbstractThe shear wave velocity of surficial sediments (VS) and the fundamental site period (TO) are important parameters for analysis of the free-field seismic response. Their spatial distribution in the Ottawa and St. Lawrence Valleys, Canada, was determined applying a standardized method consisting of (i) updating the Quaternary geology; (ii) classifying the surficial units with similar physical properties into three broad categories: upper sandy sediments, intermediate clayey sediments and basal glacial and non-glacial deposits; (iii) delineating the spatial thickness of each category by way of 3D geologic modelling; (iv) sorting of available geophysical data with respect to each individual category and assigning representative VS relationships: a power velocity-depth function for sand and clay units combined, VS=119+8.1 Depth0.5 (m/s), and a constant interval VS equal to the observed geometric mean velocity for glacial and non-glacial deposits, VS=385 (m/s). The respective TO values were computed as the ratio between the soil thickness and the average VS from ground surface to the bedrock. Validation of model results was conducted with VS and TO field data and available TO estimates from detailed urban-scale seismic zonation studies. The analyses of the uncertainty originating from the variation of the VS measurements showed that the standard deviations were roughly one-third of the modelled VS and TO values.
Summary(Plain Language Summary, not published)
A standardized method for determining of shear wave velocity and fundamental period of vibration of surficial soils was applied consisting of update of the Quaternary geology; arranging of surficial units with similar physical properties into three different categories: surficial coarse sediments (sand), intermediate fine sediments (clay) and basal glacial deposits (till); delineating the spatial variation of the thickness of each category by way of 3D geologic modeling; and choosing representative VS values. Average VS vs. depth functions were generated for sand and for clay, whereas unique interval VS value was assigned for till, Lower Palaeozoic rocks, and for Precambrian and Intrusive rocks. Respective TO was computed with the quarter-wavelength relation. Final VS and TO spatial distributions were generated at a resolution of 500 m.